In hydraulic systems having separate control valves for controlling flow into opposite ends or ports of an actuator or fluid motor, separate proportional valves or solenoid valves are required in order to control the position of the main flow spool. Naturally, this requires extra valves and associated lines and controls. Furthermore, in some systems, if there is an electrical malfunction or an electrical short in the system, the entire system is no longer functional. It is desirable to reduce the number of proportional or solenoid valves and their associated lines and controls and to provide a system in which if there is an electrical short or electrical malfunction in one part of the system that controls one actuator, the other actuators may still be operated in a normal manner.
The present invention is directed to overcoming one or more of the problems as set forth above.